Volatile Organic Compounds and Particulates as Components of Diesel Engine Exhaust Gas HANS SCHULZ,* GILBERTO BANDEIRA DE MELO, and FARID OUSMANOV Engler-Bunte-Institute, University of Karlsruhe, Kaiserstraße 12, 76128 Karlsruhe, Germany Volatile organic compounds (VOC) and soot particles have been determined in a Diesel’s exhaust gas. A new sampling method allowed the measurement of emissions of organic compounds (C 1 to C 20 ) in a gas chromatogram at a detection limit of ca. 0.2 mg/m 3 . Particles were collected with a filter bed of ceramic particles and characterized by temperature programmed desorption (TPD) and oxidation (TPO). Engine runs were always performed at a fixed and constant air to fuel equivalence ratio () and with a constant volumetric efficiency, because these parameters strongly influenced the emissions in terms of both composition and order of magnitude. The effective combustion temperature again strongly governed the nature of the emissions. Model fuels, composed of individual paraffins and aromatics and additions of sulfur compounds and an organic nitrate (for cetane number enhancement) were used. The results contribute to the understanding of the origin of specific emissions from Diesel engines. These newly developed methods are recommended for further application. © 1999 by The Combustion Institute INTRODUCTION Volatile organic compounds (VOC) in the ex- haust gas of Diesel engines have attracted much less attention than similar emissions from Otto engines [1, 2]. Commonly these emissions are only measured cumulatively and recorded in terms of propane equivalents [3]. However, they contain reactive compounds which are capable of participating in the formation of photochem- ical smog [4] and even toxic benzene is one of its significant constituents. As will be shown below, the air to fuel equivalence ratio () dominates the magnitude and composition of the emis- sions. This basic dependence is generally recog- nized in this study. In practice the air to fuel ratio (by mass) varies between  18:1 at high load conditions to  150:1 at very low load, corresponding to a range of air to fuel equiva- lence ratios from  = 1.3 to  = 11. Thus the composition of the exhaust gas from Diesel engines is very variable. The exhaust gas tem- perature (in °C) also changes by at least a factor of 2 between high and low loads. These varia- tions create a challenging task of finding prac- tical solutions for the reduction of harmful emissions. A further complication arises from sulfur in the fuel, which disturbs catalytic con- verters and also leads to both sulfuric acid and sulfates adsorbed on the particulates. Profound knowledge about the nature and the amount of emissions from Diesel engines, depending on motor-operating parameters (air to fuel equivalence ratio, volumetric efficiency, injection start, ignition delay), fuel composition (paraffins, naphthenes, aromatics, sulfur, addi- tives, boiling range, density, cetane number, nonconventional fuels) and engine design (di- rect injection, prechamber injection, number of nozzles, injection pressure, turbocharging, etc.) is important for developing systems to treat exhaust gases and for designing cleaner engines and introducing clean fuels. Additionally, basic knowledge about the nature of emissions and the parameters and modes of their formation is of interest in relation to legislative activities for emission control. EXPERIMENTAL Performance of the Measurements The measurements were conducted with a one- cylinder engine (BASF, Ludwigshafen) for test- ing cetane numbers. Some of the specifications of this engine are: displacement volume 850 ml, injection into a swirl chamber and compression ratio 18.2:1. The speed was kept at 1000 rev/min and the beginning of the injection was com- monly at 20° before top dead center. In princi- ple, every engine exhibits its individual emission *Corresponding author. COMBUSTION AND FLAME 118:179 –190 (1999) © 1999 by The Combustion Institute 0010-2180/99/$–see front matter Published by Elsevier Science Inc. PII S0010-2180(98)00146-1